The present invention relates to microfabricated therapeutic actuators, particularly to therapeutic actuators utilizing shape memory polymer (SMP) tubing and microtubing as a gripper/release mechanism, and more particularly to an SMP gripper with a release sensing system and coupling arrangements for directing light into the SMP.
Microactuators for remote and precise manipulation of small objects is of great interest in a wide variety of applications. Recently substantial efforts have been directed to the development of microactuators or microgrippers for use in the medical field, such as for catheter-based intervention therapies. There has been particular interest in the development of microactuators capable of operating in small (250-500 .mu.m) diameter applications, such as in blood vessels in the human brain, which enable catheter-based devices to reach and treat an aneurysm in the brain.
One recent approach to satisfying this need involves microactuators or microgrippers fabricated by using known silicon-based techniques or precision micromachining, or a combination of these techniques, with the microgrippers being actuated, for example, by balloons or by shape-memory alloy (SMA) films or wires deposited on or connected to the jaws of the microgrippers. Such an approach is described and claimed in U.S. Pat. No. 5,645,564 issued Jul. 8, 1997. Another recent approach involves a miniature plastic gripper constructed of either heat-shrinkable or heat-expandable plastic tubing having a cut in one end section to form gripping surfaces or jaws which are moved by inflation or deflation of an associated microballoon. Such an approach is described and claimed in U.S. Pat. No. 5,609,608 issued Mar. 11, 1997.
Patients with potentially life-threatening hemorrhagic brain aneurysms are in need of a safe, reliable, and fast release mechanism for the deposition of embolic platinum coils via catheters, such as the commercially available Guglielmi Detachable Coil (GDC). The GDC utilizes the electrolytical dissolution of a designated guidewire junction to generate the release action. This procedure typically takes 10-30 minutes and is difficult to control in a reliable fashion. Also, the effects of the dissolved material into the blood stream are a potential hazard to the patient.
A recent approach to overcome the GDC problems is to provide a delivery/release mechanism based on SMP, a polyurethane-based material that undergoes a phase transformation at a manufactured temperature (Tg) of choice. After the material is polymerized (cross-linked), the material is molded into its memory shape. At temperatures above Tg, the material can be easily reshaped into another configuration, and upon cooling below the Tg the new shape is fixed, but upon increasing the temperature to above the Tg, the material will return to its original memory shape. By inserting a GDC, for example, into an end of a SMP microtube heated to a temperature above its Tg, applying pressure to the outside of the SMP microtube to shape the tube about an end of the GDC, and then lowering the temperature below the Tg, the GDC is secured and retained in the microtube. After inserting the microtube and retained GDC via a catheter to a desired location, the SMP microtube is locally heated to above the Tg and it returns to its original shape releasing the GDC, after which the microtube is withdrawn leaving the GDC in place, without releasing any dissolved materials, etc., into the blood stream. Such an approach is described and claimed in copending U.S. application Ser. No. 08/807,412 filed Feb. 28, 1997, now U.S. Pat. No. 5,911,737 issued Jun. 15, 1999, entitled "Microfabricated Therapeutic Actuators," and assigned to the same assignee.
A more recent approach which utilizes SMP microtubing as a retention/release means for material, such as an embolic coil, provides various mechanisms for heating and cooling the SMP microtubing, including resistive heating, optical heating, and external field (RF, magnetic induction) heating, and coatings of selected materials on the microtubing. This approach is described and claimed in copending U.S. application Ser. No. 09/067,824 filed Apr. 28, 1998, entitled "Microfabricated Therapeutic Actuators and Release Mechanisms Therefor," assigned to the same assignee.
The present invention utilizes SMP tubing or microtubing as the retention/release means, as in the above-referenced copending applications, but using a laser light/fiber optic approach for releasing a coil, for example, from the SMP microtubing, a feedback or sensing system to confirm release of the coil, and coupling mechanisms of light into the SMP microtubing for heating same. The features of the present invention are incorporated into a complete catheter system, which includes a laser and control, a display panel, fiber optic components and coupler, the SMP gripper, and a release sensing or feedback arrangement.